1. Field of the Invention
The invention relates to a transmission device with switchable gear ratios, and more particularly to a transmission device applicable to a scanning apparatus and using magnetic elements in conjunction with a planet gear mechanism to switch the gear ratio.
2. Description of the Related Art
In a conventional flatbed scanning device, a driving device moves a scanning module back and forth. Usually, the moving speed of the scanning module is slower when a document is being scanned, and the moving speed of the scanning module is higher after the document is scanned and the scanning module has to be moved back to the original position in order to shorten the time of the overall scanning process. In addition, the moving speeds of the scanning module for scanning with a high resolution and a low resolution are also different. Thus, it is preferred that the output speed of the driving device may be changed.
In the conventional scanning device, an additional motor or an additional driving device is utilized to switch the gear ratios of power transmitting elements, such as gears in a gear set, so that the output speed may be changed. However, the added motor or driving device occupies extra space in the scanning device, which is disadvantageous to the miniaturization of the scanning device.